1. Field of the Invention
The present invention relates to an image pickup apparatus, and in particular to an image pickup apparatus having a CCD (Charge-Coupled Device) type of image pickup device converting incident light to a corresponding image signal for correcting a transfer error. The present invention also relates to a method therefor.
2. Description of the Background Art
Conventionally, a multitude of various reading methods for reading out data at a high rate in a CCD-type image pickup device have been proposed. In particular, Japanese patent laid-open publication No. 244340/1993 proposes a branched-outlet type of CCD image pickup device comprising: a plurality of photosensitive cells for converting incident light to electrical charges; a first charge transfer path for transferring in one direction the electric charges read out from the photosensitive cells; a shift gate for transferring the electrical charges generated in the photosensitive cells to the first charge transfer path; a second charge transfer path connected via an output gate to the first charge transfer path; a first output portion connected to the output end of the second charge transfer path; a third charge transfer path connected to the output gate for transferring the electric charges in a direction different from the direction of the electric charges transferred over the second charge transfer path; and a second output portion connected to the output end of the third charge transfer path, the output gate being turned on during high speed driving to alternately output a signal from the first and second output portions, or the output gate being turned on during low speed driving to output a signal only from the first output portion.
This conventional configuration is based on the concept that since in a CCD-type image pickup device having only one output portion, it is difficult to drive the final stage amplifier producing an output and a CDS (Correlated Double Sampling) circuit subsequent to the amplifier at high frequency, two or more final stage amplifiers and CDS circuits are provided in the CCD-type image pickup device having a plurality of output portions in order to reduce the driving frequency by one half.
In addition to the CCD-type image pickup device disclosed in the above JP patent publication, a right-and-left separation type of CCD image pickup device has been proposed. The term “right-and-left separation type of CCD image pickup device” means that signal charges generated in the right and left halves of the photosensitive cell array of an image pickup device are transferred over different horizontal transfer paths in right and left directions and read out therefrom, respectively. However, since the signal charges of the right and left halves of the photosensitive cell array of the image pickup device are separately read out, a difference in property between the amplifiers provided at the output ends of the right and left horizontal transfer paths and a difference in property between the right and left horizontal transfer paths cause a vertical split to be viewed in the center of a frame of image.
The branched-outlet type of CCD image pickup device disclosed in the above JP patent publication operates so that horizontally transferred signal charges are alternately assigned to the two horizontal transfer paths and amplifiers during transfer of signal charges. Therefore, the image pickup device may be designed such that the electric charges representative of specific colors are assigned to the corresponding horizontal transfer paths and amplifiers, thus allowing a white balance adjustment to be performed to compensate for the difference in property between the horizontal transfer paths and amplifiers.
However, when signal charges developed from a single horizontal transfer path are in turn assigned to two horizontal transfer paths, an assignment error occurs, thereby causing a phenomenon such as appearance of a vertical stripe, angled stripe, and color mixing in an image to be viewed. Particularly, when the temperature of the image pickup device changes, an additional problem occurs that an assignment error varies depending on the change in temperature.